The present invention relates to apparatus for casting molten metals and, more particularly, to protective inserts or nozzles which have through bores and which are disposed in the outlet passageways of a casting ladle to protect the surfaces of the outlet passage from wear and deterioration that would result from contact with the molten metal.
In the field of handling molten materials, there is occasion to employ nozzles or casings in a variety of instances, for example, not only with casting ladles, but also in intermediate containers and distribution chutes or at the ends of funnels in order to protect the outlet passageways of such elements against wear and deterioration. To this end, the prior art has suggested the use of pipes in the form of funnels, or specially prepared blocks or bricks which are set in place in the outlet passages of the molten metal containers.
Since the protective inserts for the outlet passageways of such containers are exposed to the heat of the molten metal directly, over a period of time, replacement of such inserts becomes necessary. In the production of the materials for the containers and protective inserts or nozzles, in order to reduce manufacturing costs, considerable inaccuracies are tolerated, particularly since mortar material can be employed to form the joints between the assembled parts and, in any event, since the precise fit between such parts are impossible to obtain on a commercial scale. Accordingly, depending on the quality of the mortar material employed, such mortar material must serve not only to fill the joints between the parts, but also must have sufficient strength when solidified as to resist mechanical stresses which are built up between the joined bodies.
This is particularly true where the mortar joints are disposed between two engaging bodies which have variable expansion characteristics at the temperatures experienced in a molten metal casting operation. Specifically, in the case of a nozzle for a casting ladle through which molten metal flows, the insert or nozzle shields the outlet passage from direct contact with the molten metal so that the expansion of the insert will naturally be greater, since it is directly exposed to the molten metal, than any expansion that occurs in the outlet passage of the ladle itself. In such environments, the mortar material which, in general, has a higher plasticity than the nozzle, as well as the outlet passage of the ladle which is at a lower temperature, can serve as an equalizing layer which will distribute forces of expansion originating in the nozzle and thus, tends to prevent any damaging of the outlet passage of the casting ladle or the casting ladle itself.
Apart from the fact that damage to the casting ladle outlet passage is avoided by the use of mortar in the joint between the passageway and nozzle, it is still very difficult to assure the exact centering of the nozzle insert in the outlet passageway due chiefly to the fact that the casting ladle itself, as well as its outlet passageway, are at an elevated temperature.
Another difficulty that has been encountered arises during the application of the mortar to one or the other of the surfaces to be joined together. In general, the adhesion of the relatively stiff mass of mortar to the surfaces is relatively great due to the very rough character of these surfaces which are made of fire-resistant material. This characteristic of the surfaces also renders even distribution of the mortar on the surfaces complicated.
One well known problem that has been long encountered in this field is the difficulty of properly proportioning the quantity of mortar on one or the other of the surfaces so as to allow the proper insertion of the protective insert or nozzle into the outlet passageway. An improper distribution or proportioning of the quantity of mortar will obviously affect adversely the centering of the insert in the outlet passageway and may result, when the mortar hardens, in a deviation in the position of the nozzle in the passageway, both with respect to the axial position as well as its transverse position. This problem is accentuated by the fact that when mortar comes into contact with the hot casting ladle passageway, it begins to immediately set up to form a bond which renders repositioning of the insert or nozzle difficult, if not impossible. Cooling of the casting ladle outlet passage is impractical since it must be done very slowly to avoid cracking of the material.
As a result of these conditions, it has become necessary to apply the entire quantity of mortar material to the exterior surface of the nozzle insert. However, upon pushing the nozzle insert thus coated with mortar material into the outlet passageway of the casting ladle, invariably portions of the mortar are stripped away, particularly at the innermost portion of the passageway thus resulting in the undesirable condition that the innermost portion of the joint will not be filled with mortar material. As a result, the achieving of a stable seating of the insert nozzle will not be assured.
Another danger that results from the condition described above exists where the mortar material itself is exposed to the flow of molten metal since, here, the mortar must function to prevent the flow of molten metal through the joint. Thus, it can be appreciated, where the joint is not completely filled with the mortar, not only is part of the passageway exposed to the molten metal, but there is a substantially increased danger that the mortar material will be washed out. This is particularly dangerous when one considers that in many circumstances, it is not possible to visually inspect the interior filling of the joint.
The present invention has for its primary object to overcome the foregoing difficulties by providing novel means for carrying the mortar material on the exterior surface of the nozzle insert to facilitate the insertion of the nozzle and mortar material into the outlet passage of a molten material container.
The present invention takes advantage of the fact that conventionally, the thickness of the mortar joint is sufficiently large so as to assure the production of a sufficiently strong joint. Thus, the novel protective insert for a nozzle can be employed in already existing casting apparatus.
In summary, according to the present invention, the protective insert or nozzle is in the form of a truncated cone having a through bore or passageway where the conical surface portion of the insert is provided with raised surfaces or ridges having specific dimensions.
By raised surfaces, it is to be understood in the context of the present invention, such elevation, the dimensions of which exceed the normally rough surfaces found on such materials as a result of conventional production procedures and which do not exceed the thickness of the joint or gap which, in the past, has ideally been fully occupied by mortar material.
By virtue of the provision of the raised portions, ridges or projections on the exterior surface of the truncated cone, according to the present invention, not only is the application of mortar onto this surface facilitated, but also the proportioning and distribution of the mortar material over the exterior surface of the nozzle is made easier since the spaces between the raised portions will be entirely filled with mortar material. Accumulations of mortar can occur with this arrangement only at a distance greater than the heigth of the projections from the surface of the truncated cone. The adherence of the mortar to the surface of the protective insert provided with the raised surface portion is enhanced which will naturally have an effect on the residual thickness of the mortar layer. This will materially contribute to assuring that the mortar joint, when the elements are assembled, will be completely filled.
One of the chief advantages of the development of the present invention resides in the fact that it now will be possible to properly center the nozzle directly into the outlet passageway of the casting ladle thus minimizing the possibility of uneven expansion of the nozzle insert causing damage to the adjoining elements of the casting ladle.
Thus, according to the present invention, the raised portions or elevations on the surface of the truncated cone of the protective nozzle insert facilitate distribution and proportioning of the mortar over the surface of the insert as well as facilitate carrying of the mortar material into the outlet passageway on the exterior surface of the insert and also serve to assure proper centering of the cone-shaped insert in the outlet opening of the casting ladle. Additionally, it will be noted that these raised surface portions will occupy a portion of the joint volume itself, thus decreasing the danger of perforation or washing out of the mortar material by the molten metal.